Developing apparatus for the silver salt diffusion process



Nov. 6, 1962 w. LAssle 2,

DEVELOPING APPARATUS FOR THE SILVER SALT DIFFUSION PROCESS Filed July 28, 1959 INV EN TOR.

WOLFGANG LA'ss/G A TTORNEYS United States The present invention relates to a developing apparatus suitable for carrying through the silver salt diffusion process. According to this process an imagewise exposed silver halide emulsion layer (negative layer) is developed in a silver halide developing solution in the presence of a silver halide solvent and brought into close contact with a transfer layer (positive layer) whereby a negative silver image of the original to be reproduced is formed in the silver halide emulsion layer and unexposed silver halide of said negative layer is dissolved and transferred to said positive layer where it is reduced to form a positive silver image of the original.

Numerous constructional forms of developing apparatus for carrying through the silver salt diffusion process are known in which apparatus the guiding of negative and positive papers through the developer liquid to a pair of wringer rollers is assured by so-called guide elements. These guide elements usually consist of a number of plates or strips made of corrosion-resisting material, such for example as plastics. These plates or strips are more or less curved, but may sometimes be also straight, depending on the type of apparatus, and are arranged one above the other over the full width of the paper insertion slots. They enable the negative and positive papers to be introduced separately, and both papers to be fully and adequately wetted in the developer. The guide elements are so formed that they guide the papers together once wetting has taken place. The lower guide element terminates just in front of the rollers and serves for the purpose of finally introducing the papers into the pair of rollers.

In these apparatus, the negative and positive papers in the developer solution are deflected by the guide elements, which always leads to certain degrees of torsion in the individual sheets. Even with the most skilful handling, it is not always possible to avoid copies appearing distorted or on askew. With a single copy, this defect is not important, since subsequent correction can always easily be efiected by trimming.

However, this correction does not apply to the offset printing foils recently brought on to the market, in which a silver image is produced on a metal plate, coated paper or plastic foil by the silver salt diffusion process, and is subsequently prepared in order that ink may be applied. Since the usual offset printing machines, which are used mainly in offices and on which the printing by means of the diffusion foils is carried out, only provide for possibilities of correction in the vertical and lateral displacement of the printing image, but not for diagonal compensation, a correction is only possible here with the prints, which is only possible by loss of the most desirable use of the format of the printing paper and thus with considerable expense. By this means, the economic value of the foils is greatly reduced.

This defect can be avoided in principle, and in addition an accurate adaptation of the picture to be copied can be obtained with respect to the vertical and lateral position, if the two materials, that is to say the negative paper and the offset foil in this case, are firmly united at the edge which is the first to enter the wringer rollers prior to development. This can be effected in any desired manner, but most simply by applying an adhesive strip from the back of the offset foil to the perforations, so that the negaatent tive paper can be attached to the adhesive strip through these perforations.

However, experience shows that a negative paper firmly united to the offset foil in this way can no longer be processed satisfactorily in the conventional developing apparatus, because it is now impossible for the materials to be separately inserted by way of the guide elements, and consequently an incomplete moistening by the developer, is usually only achieved at the margins.

It has now been found that these difliculties can be overcome by means of a developing apparatus for the silver salt diffusion process, which apparatus has a guide element consisting of lateral guide rails for the photographic materials.

The construction and operation of these guide rails are explained by way of example by reference to the accompanying drawings in which:

FIG. 1 is a composite view including FIGS. 1A and 1B;

FIG. 1A is a cross-sectional view taken through FIG. 1B along the lines 1A1A;

FIG. 1B is a front view in elevation of one embodiment of this invention;

FIG. 2 is a composite view including FIGS. 2A-2E;

FIG. 2A is a plan view of a piece of negative paper which is developed in the apparatus of FIG. 1;

FIG. 2B is a perspective view of a piece of foil which passes through the apparatus shown in FIG. 1 in conjunction with the negative paper shown in FIG. 2A; and

FIGS. 2C-2E are perspective views of the aforementioned negative paper and foil in various relative positions.

FIG. 1 is a view of one embodiment of the developing apparatus according to the invention. This developing apparatus has a conventional lower guide element 1, which is so curved that the papers are directed towards the wringer rollers 3 after having travelled through the developer 2. These wringer rollers are preferably so arranged that the contact line of the two rollers is above the level of the developer liquid. Above said guide element 1 a guide rail 5 is arranged on each of the two sides of the feed slot 4, each rail 5 consisting of plastic or other non-corrosive material, and preferably projecting from the said slot. On the upper side, the feed slot is so closed by an additional guide element 6 that the latter forms at the margins with the previously described guide rails 5, an insertion channel 7 for the sheet which is uppermost during development. Instead of the guide element 6, another guide rail corresponding to 5 can be used for forming this channel.

The manner in which development is carried out is illustrated in FIG. 2. First of all in FIG. 2A, the two upper corners 8 are cut off at an angle from the lightsensitive negative paper 9. A strip of adhesive tape 10 is then applied to the back of the offset foil 11 over the perforations 12, as shown in FIG. 2B. The exposed negative paper 9 is then stuck to the front of the foil 11 With the silver halide layer facing the foil 11 and in the correct position by means of the adhesive strip 10 acting through the perforations 12, as shown in FIG. 2C. Thereupon, as shown in FIG. 2D, the negative 9 is shown folded back once beyond the adhesive edge and creased to form a leading edge 13. With the bending back of the negative 9, a curvature 14 is formed, as shown in FIG. 2E, which now permits the cut corners 8 of the papers to be so fed on to the guide rails that the offset foil 11 engages in the lower portion of guide channel 7, while the negative 9 is lifted by the guide rails 5 and conducted separately through the developer to thoroughly wet both of them. Since the curvature 14, once it is formed, is maintained over the area of the negative paper 9 throughout the entire travel period, a rigidity is imparted to these papers. The rigidity is sufficient to prevent an otherwise possible collapse or buckling in the longitudinal direction during the travel period. For this reason, the free space SP. between the guide rails shown in FIG. 16 is about 1 to 5 cm. less than the width of the negative paper 9, and corresponds substantially to the length of the adhesive edge which remains after cutting off the corners of the negative. The papers are guided through the developer to the rollers and reach the latter in the condition provided by the adhesive connection. With an appropriate arrangement of the guide rails, the papers are also just gripped and are pulled through without distortion by the rollers.

The guide rails 1, 5 and 6 have their entrances disposed above the liquid level in the development apparatus and slope downwardly together until they extend below the liquid level. From a point below the liquid level outer guide elements 1 and 6 extend upwardly from the liquid and converge toward the pair of wringer rollers 3. However, central guide element 5 terminates beneath the liquid level to permit negative paper '9 and foil 11 to move into contact with each other prior to entering between the wringer rollers. The transition of guide elements 1 and 6 from their downward to upward directions is curved to smoothly guide the sheet materials toward wringer rollers 3, and the lower surface 15 of central guide element 5 is also curved for this same purpose. Particularly eifective guidance for the sheet materials is provided by slightly diverging elements 1 and 6 as they pass into the liquid and then converging'them as they approach wringer rollers 3. This guidance is further facilitated by increasing the thickness of central guide element 5 as it enters the liquid and forming the lower surface of its extremity beneath the liquid in a smooth curve.

What is claimed is:

1. An apparatus for developing photographic materials including a negative sheet material and a transfer material joined to each other at a portion of their leading edges to leave the sides of said leading edges free, said apparatus comprising a container for holding developing liquid, said container having a pair of substantially vertical side walls, three spaced guide elements extending laterally from and between said side walls to provide between them a pair of slots for insertion of said meterials, the upper and lower of said guide elements extending longitudinally between an entrance and an exit disposed above the level of said liquid with an intermediate section in which the space between said upper and lower guide elements is disposed within said liquid, wringer means disposed at said exit, the central of said guide elements including a pair of rails extending a short distance from each of said side walls between said upper and lower guide elements with a free space extending laterally between adjacent sides of said rails, and said rails terminating a short distance before said exit to permit said wringer means to press together said negative and transfer materials which have been separated in their passage through said slots and said liquid by insertion of said rails between said free sides of said leading edges.

2. An apparatus as set forth in claim 1 wherein said upper and lower guide elements gradually diverge from each other in a direction from said entrance to said intermediate section and gradually converge in a direction from said intermediate section to said wringer means.

3. An apparatus as set forth in claim 2 wherein said rails increase in thickness in a direction from said entrance to said intermediate section, and said rails terminate to dispose their extremities in said intermediate sectionbetween said inner and outer guide elements.

4. An apparatus as set forth in claim 3 wherein the lower surfaces of said extremities are smoothly curved to help guide said negative and said transfer material smoothly together.

References Cited in the file of this patent UNITED STATES PATENTS 2,786,401 Briggs et al Mar. 26, 1957 FOREIGN PATENTS 699,085 Great Britain Oct. 28, 1953 

